The ASTM B265 grade 5 chemical specifications for 6/4 require that vanadium is present in the amount of 4%±1% by weight and aluminum is present in the range of from about 5.5% to about 6.75% by weight. The alloy of the invention is produced by the Armstrong Process as previously disclosed in U.S. Pat. Nos. 5,779,761; 5,958,106 and 6,409,797, the entire disclosures of which are herein incorporated by reference. The aforementioned patents teach the Armstrong Process as it relates to the production of various materials including alloys. The Armstrong Process includes the subsurface reduction of halides by a molten metal alkali or alkaline earth element or alloy. The development of the Armstrong Process has occurred from 1994 through the present, particularly as it relates to the production of titanium and its alloys using titanium tetrachloride as a source of titanium and using sodium as the reducing agent. Although this invention is described particularly with respect to titanium tetrachloride, aluminum trichloride and vanadium tetrachloride and sodium as a reducing metal, it should be understood that various halides other than chlorine can be used and various reductants other than sodium can be used and the invention is broad enough to include those materials.
However, because the Armstrong Process over the past eleven years has been developed using molten sodium and chlorides, it is these materials which are referenced herein. During the production of titanium by the Armstrong Process, as disclosed in the previous patents, the steady state temperature of the reaction can be controlled by the amount of reductant metal and the amount of chloride being introduced. Although it is feasible to control the reaction temperature by varying the chloride concentration while keeping the amount of molten metal constant, the preferred method is to control the temperature of the reactant products by varying the amount of excess (over stoichiometric) reductant metal introduced into the reaction chamber. Preferably, the reaction is maintained at a steady state temperature of about 400° C. and at this temperature, as previously disclosed, the reaction can be maintained for very long periods of time without damage to the equipment while producing a relatively uniform product.
Heretofore, commercially pure (CP) titanium ASTM 8265 grades 1, 2, 3 and 4 have been produced in over two hundred runs using the Armstrong Process and although a wide variety of operating parameters have been tested, certain results are inherent in the process. The ASTM B 265 spec sheet follows:
TABLE 1Chemical RequirementsComposition %GradeElement12345678910Nitrogen max0.030.030.050.050.050.050.030.020.030.03Carbon max0.100.100.100.100.100.100.100.100.100.08HydrogenB max 0.015 0.015 0.015 0.015 0.015 0.020 0.015 0.015 0.015 0.015Iron Max0.200.300.300.500.400.500.300.250.200.30Oxygen max0.180.250.350.400.200.200.250.150.180.25Aluminum————5.5 to4.0 to—2.5 to——6.756.0—3.5——Vanadium————3.5 to——2.0 to4.53.0Tin—————2.0 to————3.0————Palladium——————0.12 to—0.12 to—0.250.25Molybdenum—————————0.2 to 0.4Zirconium——————————Nickel—————————0.6 to 0.9Residuals C.D.E.0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 (each), maxResiduals C.D.E.0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 (total) maxTitaniumFremainderremainderremainderremainderremainderremainderremainderremainderremainderremainderA Analysis shall be completed for all elements listed in this Table for each grade. The analysis results for the elements not quantified in the Table need not be reported unless the concentration level is greater than 0.1% each or 0.4% total.BLower hydrogen may be obtained by negotiation with the manufacturer.C Need not be reported.D A residual is an element present in a metal or an alloy in small quantities inherent to the manufacturing process but not added intentionally.E The purchaser may, in his written purchase order, request analysis for specific residual elements not listed in this specification. The maximum allowable concentration for residual elements shall be 0.1% each and 0.4% maximum total.FThe percentage of titanium is determined by difference.
Production of titanium powder by the Armstrong Process inherently produces powder in which the average diameter of individual particle is less than a micron. During distillation at 500 to 600° C., the particles agglomerate and have an average agglomerated particle diameter in the range of from about 3.3 to about 1.3 microns. Particle diameters are based on a calculated size of a sphere from a surface area, such as BET. For agglomerated particles, the calculated average diameters were based on surface are measurements in a range of from about 0.4 to about 1.0 m2 per gram. In over two hundred runs, the titanium powder produced by the Armstrong Process always has a packing fraction in the range of from about 4% to about 11% which also may also be expressed as tap density. Tap density is a well known characteristic and is determined by introducing the powder into a graduated test tube and tapping the tube until the powder is fully settled. Thereafter, the weight of the powder is measured and the packing fraction or percent of theoretical density is calculated.
Moreover, during the production of CP titanium by the Armstrong Process, a certain amount of sodium has always been retained even after extensive distillation, including vacuum distillation, and this retained sodium has been present on average of about 500-700 ppm, and has rarely been below about 400 ppm. From a commercial point of view, significant effort is and has been expended in order to reduce the sodium content of CP titanium made by the Armstrong Process.
Prior to the Armstrong Process, CP titanium powder and titanium alloy powder traditionally have been made by two methods, hydride-dehydride and spheridization, resulting in powders having very different morphologies than the powder made by the Armstrong method. Hydride-dehydride powders are angular and flake-like, while spheridized powders are spheres.
Fines made during the Hunter process are available and these also have very different morphology than CP titanium produced by the Armstrong Process. SEMs of CP powder made by the hydride-dehydride process and the spheridization process and Hunter fines are illustrated in FIGS. 1 to 3, respectively. The CP powder made by the Armstrong Process is not spherical nor is it angular and flake-like. Hunter fines have “large inclusions” which do not appear in the Armstrong powder, differentiating FIGS. 1-3 from Armstrong powder shown in FIGS. 4-9. Moreover, Hunter fines have large concentrations of chlorine while Armstrong CP powder has low concentrations of chlorine; chlorine is an undesirable contaminant.
6/4 powder is made by hydride-dehydride and spherization processes, but not by the Hunter process. A calcium reduction hydride-dehydride process used in Tula, Russia was identified by Moxson et al. in an article in The International Journal Of Powder Metallurgy, Vol. 34, No. 5, 1998. Moxson et al which also discloses SEMs of both CP and 6/4 in the Journal Of Metallurgy, May, 2000, both articles, the disclosures of which are incorporated by reference, taken together showing that 6/4 powder made by methods other than the Armstrong process result in powders that are very different from Armstrong 6/4 powder, both in size distribution and/or morphology and/or chemistry. In some cases, such as the calcium reduction process in Tula, Russia there are very significant differences in chemistry as well as the other differences previously mentioned. Both the hydride-dehydride and spheridization methods require Ti, Al and V to be mixed as liquids and thereafter formed into powder. Only the Armstrong Process produces alloy powder directly from gas mixtures of the alloy constituents.
Because 6/4 titanium is the most common titanium alloy used by the Department of Defense (DOD) as well as the aerospace industry and other significant industries, the production of 6/4 by the Armstrong Process is an important commercial goal.